The hypercellular-hypertrophic form of human obesity is exceedingly refractory to treatment. The major goals of this research are to use the genetically obese hypercellular-hypertrophic Zucker fafa rat, and hormonally manipulated normal rats, as models to examine the development of both the behavioral and metabolic correlates of genetic obesity. First, the relationship between adipose tissue cellularity and lipoprotein lipase (LPL) activity and the development of hyperphaqia and food motivated behavior in the fatty rat will be examined. Second, the effect of pharmacological interventions on metabolic factors in genetic obesity will be determined. Third, the effects of LPL activity and blood metabolite levels on short and long term nutrient preferences in the fatty rat will be examined. Fourth, the effects of intragastric preloading, and the clearance and uptake of infused nutrients on feeding behavior in the fatty rat will be measured. In short, the goals of the proposed research are twofold: (1) basic, i.e., to increase our understanding of the origin of hypercellular-hypertrophic obesity, and (2) applied, i.e., to develop strategies which may be applicable to the human obese condition and useful in potential intervention studies.